Gas turbine engines may be used to power various types of vehicles and systems, such as air or land-based vehicles. In typical gas turbine engines, compressed air generated by axial and/or radial compressors is mixed with fuel and burned, and the expanding hot combustion gases are directed along a flowpath and through a turbine nozzle having stationary vanes. The combustion gas flow deflects off of the vanes and impinges upon turbine blades of a turbine rotor. A rotatable turbine disk or wheel, from which the turbine blades extend, spins at high speeds to produce power. Gas turbine engines used in aircraft use the power to draw more air into the engine and to pass high velocity combustion gas out of the gas turbine aft end to produce a forward thrust.
In the development and testing of new designs for gas turbine engine components, it is important to minimize the amount of time required to manufacture “critical path components,” like cooled turbine blades and vanes. In high performance gas turbine engine applications, these cooled turbine blades and vanes are typically manufactured using superalloy materials and casting processes to produce a single crystal or polycrystalline material. For example, cast turbine blades and vanes can be made by means of directional solidification of a liquid melt pool that is in the shape of the article. The melted alloy in the shape of the article is then slowly solidified from one end by a process that extracts heat in the direction in which the fast growing grains are desired to be oriented in its preferred growth direction. The growth of these fast growing grains naturally occurs in the crystallographic direction with the miller indices of <001>.
However, for the above-noted purposes of development and testing, the casting process takes an undesirably long time and involves (i) making core dies, cores, wax dies, wax patterns, and ceramic molds with an inner cavity in the form of the article, (ii) a melt furnace of sufficient inner volume in which the alloy can be completely melted, (iii) a ceramic sieve to filter out unwanted ingredients in the melt pool, and (iv) a heated furnace with heat extraction capabilities. As such, it should be appreciated that the investment for this assembly of equipment is large, and the lead time to make the first article takes many months. This prior art casting process is too expensive and too time consuming for fast-paced and/or low volume development programs.
Hence, there is a need for manufacturing methods that allow for the production of metallic articles, such as gas turbine engine components, which exhibit properties that are the same as or similar to traditionally-cast directionally-solidified articles, yet which do not require the time and expense of traditional casting processes. Furthermore, other desirable features and characteristics of directionally recrystallized microstructure in additively-manufactured metallic articles, and the method for manufacturing the same will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the preceding background.